Apparatus for feeding bonding wire

ABSTRACT

An apparatus is described for maintaining and delivering a slack reserve length of lead wire between a spool or other source and the wire bonding tool of a lead wire bonding machine. A slack chamber or wind chamber comprised of a housing enclosure, an inlet guide on one side for guiding lead wire into the slack chamber from a spool, an outlet guide on the other side for guiding lead wire out of the slack chamber towards the wire bonding tool maintains the reserve length of lead wire in untangled condition. A source of pressurized dry air or other gas directs a gaseous flow into the slack chamber so that the lead wire is maintained suspended in the gaseous flow in an offset configuration. Wire sensors are operatively positioned in the slack chamber for sensing the offset of lead wire in the wind stream. The wire sensors are coupled to sensor and control logic for controlling the delivery and feeding of lead wire from a spool into the slack chamber. The wire sensors define inner and outer limits of offset thereby maintaining the reserve length within a desired range. Additional elements for back-up control of the lead wire and for handling the spool are described.

This is a division of application Ser. No. 507,340, filed June 24, 1983,now U.S. Pat. No. 4,498,638 issued Feb. 12, 1985.

TECHNICAL FIELD

This invention relates to new apparatus for maintaining and delivering aslack reserve of lead wire between a spool or other source and the wirebonding tool of a lead wire bonding machine. The invention hasparticular application for lead wire bonding machines used in bondinglead wires between a microcircuit chip and the lead frame on which thechip is mounted for coupling to external circuitry. The inventionprovides controlled maintenance of slack reserve capillary lead wiresufficient for automated and multiple bonding operations and for feedingand delivery of the slack reserve lead wire in untangled and slightlytensioned condition.

BACKGROUND ART

Integrated circuit or microcircuit chips are generally mounted on leadframes for coupling to external circuitry. Lead wires are bonded betweendie pads on the microcircuit chip and the lead frame fingers usingmanual or automatic ball bonding machines. The fine lead wire isgenerally stored on a stationary spool. The wire is drawn off the end ofthe spool and fed through a capillary wire holding tool or bonding toolwhich performs successive multiple bonding operations. Typically, oneend of the lead wire is bonded to a die pad of the integrated circuitchip using ball bonding methods. The other end of the lead wire isbonded to a lead frame finger using a wedge bond or weld.

An example of a manual ball bonding machine is the Kulicke & SoffaIndustries, Inc. (K&S), Model #478, which is actually a semi-automaticmachine. The capillary wire holding or bonding tool is manuallypositioned by an operator viewing through a microscope objective. Thebonding itself is then performed by an automatic operation of the ballbonding machine. However, manual positioning and monitoring slows downthe lead wire bonding operation. A modification and further descriptionof the manual or semi-automatic ball bonding machine is found in U.S.patent application, Ser. No. 294,411, filed Aug. 19, 1981 for LEAD FRAMEWIRE BONDING BY PREHEATING, by the same assignee as the presentapplication.

The fully automatic lead wire bonding machine greatly increases thespeed of the lead wire bonding and chip packaging operation. An exampleof the automated ball bonding machine or robot is the Kulicke & SoffaIndustries, Inc. (K&S), Model #1419, Hi Speed Ball Bonder. Amodification of this ball bonding machine for fully automatic errorcorrecting robot operation is described in U.S. patent application, Ser.No. 470,217, filed Feb. 28, 1983 for LEAD WIRE BOND ATTEMPT DETECTION,filed by the same inventive entity and assignee as the presentapplication.

With the advent of high speed automatic ball bonding machines and robotsa difficulty is encountered in feeding the fine capillary lead wire fromthe source such as a spool to the capillary wire holding and bondingtool. In present bonding machines such as the K&S models referred toabove, the capillary bonding wire is stored on a spool approximately twoinches (5 cm) in diameter and about one inch (2.5 cm) in length. Thespool is mounted in a stationary position and is designed to permit thefine wire to be fed off the end in a direction parallel to the axis ofthe spool. This has proved satisfactory for the slower operation manualbonding machines. For the high speed bonding machines, however, thelength of wire stored on the spool is inadequate requiring frequentreplacement. The lead wire is normally stored in a single layer to avoiddeformation or entanglement of the fine metal wire which may be, forexample, a fine gold wire or copper wire 0.001 inches (0.0254 cm) indiameter. For storage of greater length attempts have been made to windmultiple layers of wire on the spool. A disadvantage of this method isthat forces from overlying layers tends to deform the underlying layerswhen wire from the outer layer is drawn from the end of the spool.

Another disadvantage of the conventional method of storing and feedingthe fine capillary lead wire is that the wire may twist and turn as aresult of torquing forces in the wire itself produced by drawing thewire from the end or top of the stationary spool in the directionparallel to the axis. Thus, for example, it is noted that the lead wiremay twist and turn in the capillary wire holding bonding tool andinterfere in the bonding operations.

A further disadvantage of the traditional methods of storing and feedingbonding wire in the automatic ball bonders results from the high speedoperation. The multiple bonding steps at high speed requires that areserve of lead wire be maintained and available for feeding directlyinto the bonding tool in steps of rapid succession to match the highspeed of the bonding steps. The conventional ball bonding machinesafford no such slack reserve of lead wire sufficient for the high speedautomatic operation nor can they assure feeding of lead wire at highspeed without becoming tangled, or distorted or deformed.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide a newapparatus for maintaining and feeding bonding lead wire which maintainsa slack reserve of lead wire sufficient for high speed fully automaticbonding machines and robots and for high speed multiple bondingoperations.

Another object of the invention is to provide apparatus for maintainingin bonding machines and robots of the automatic type a slack reserve oflead wire within a predetermined range of length in untangled condition,for delivery to a capillary bonding tool without distortion ordeformation of the fine lead wire.

A further object of the invention is to provide a system for maintainingadequate reserve of lead wire ready for high speed multiple bondingoperations in slightly tensioned condition with automatic sensing andcontrol of the rate of delivery, and for controlled feeding of lead wirefrom a spool without distortion or deformation.

DISCLOSURE OF THE INVENTION

In order to accomplish these results the present invention provides anovel slack chamber arrangement for maintaining a reserve of lead wirein untangled condition. The slack chamber comprises a housing enclosure,an inlet guide on one side for guiding lead wire into the slack chamberfrom a spool, an outlet guide formed on the opposite side of the housingenclosure for guiding lead wire out of the slack chamber towards thewire bonding tool, and wire sensors operatively positioned for sensingthe offset of lead wire passing through the slack chamber from the inletguide to the outlet guide. A source of pressurized dry air or other gasis provided adjacent the slack chamber at a location between the inletand outlet guide for directing a gaseous flow into the slack chamber inthe direction of the wire sensors. A length of lead wire passing throughthe slack chamber between the inlet guide and outlet is therebymaintained and suspended in the gaseous flow in a configuration offsetfrom an imaginary line joining the inlet and outlet guides. In thismanner a slack reserve of lead wire may be maintained under slighttension for delivery in untangled and undistorted condition to thebonding tool.

According to another aspect of the invention a wire feed control isprovided operatively coupled to receive control signals from the wiresensors for controlling the delivery and feeding of lead wire from aspool into the slack chamber in response to the signals. The length ofthe slack reserve of lead wire under slight tension may therefore becontrolled and maintained within a predetermined range. A feature andadvantage of the apparatus according to the present invention is thatthe lead wire is fed from a rotating spool mounted on a spool holder forcontrolled rotation in response to control signals from the wiresensors. The wire is delivered from the spool without twisting orturning as occurs when the wire is drawn from the end of the spool anddistortion and deformation are further eliminated by feeding the wire ina direction generally perpendicular to the axis of the spool and tangentto the cylindrical surface of the spool.

According to a preferred embodiment of the invention, the apparatusincludes a spool holder or mounting device, a spool drive motor coupledto the spool mounting device for driving the device and rotating amounted spool, and control logic operatively coupled to the spool drivemotor for turning the motor on and off and thereby advancing lead wirefrom the spool in predetermined increments. The slack chamber housingincludes top and bottom plates spaced apart with side walls and leadwire inlet and outlet guides juxtaposed in opposing side walls.

For the wire sensors the invention contemplates providing a plurality ofoptical sensors arranged in a row substantially perpendicular to andoffset from an imaginary line connecting the inlet and outlet guides ofthe slack chamber. The optical sensors are operatively coupled togenerate control signals for the control logic at the spool drive motor.The row of optical sensors in the preferred embodiment includes an innerlimit optical sensor and an outer limit optical sensor arranged todefine an inner and outer limit of offset of the lead wire maintained bythe flow of gas directed into the slack chamber in the direction alongthe row of optical sensors. The reserve length of lead wire suspended inuntangled condition in the flow of gas is thereby maintained within adesired range.

The inner limit optical sensor defining the inner limit of offset of thelead wire in the slack chamber is operatively coupled to the controllogic for turning on the spool drive motor when the lead wire is sensedin the vicinity of the inner limit optical sensor thereby deliveringfurther reserve lead wire to the slack chamber. The outer limit opticalsensor is operatively coupled to turn off the spool drive motor when thelead wire is sensed in the vicinity of the outer limit optical sensor sothat the length of reserve lead wire is maintained in the slack chamberwithin the desired range. For the row of optical sensors the inventioncontemplates a first row of optical sources mounted along one plate ofthe slack chamber housing enclosure and a corresponding row of opticaldetectors mounted along the opposite plate of the slack chamber andaligned with the restrictive optical sources.

According to another feature of the invention a plurality of back-upoptical sensors are provided along the row for redundancy and safety incontrolling delivery of lead wire. For example, a bond machine stopoptical sensor is mounted in the row of optical sensors before one ormore inner limit optical sensors, and is operatively coupled for turningoff the bonding machine if the lead wire offset is reduced to the pointwhere the lead wire is sensed in the vicinity of the bond machine stopoptical sensor. A spool drive motor stop optical sensor may also bemounted along the row of optical sensors beyond one or more outer limitoptical sensors for shutting off the spool motor if excessive reserve oflead wire occurs in the slack chamber and the lead wire is sensed in thevicinity of the spool motor stop optical sensor. A feature and advantageof using such a row of multiple optical sensors is that the bond machinestop optical sensor serves as a back-up safety for the inner limitoptical sensors at the shorter limit of slack reserve maintained in theslack chamber. The spool drive motor stop optical sensor serves as aback-up safety for the outer limit optical sensors in controlling theouter range or longer limit of slack reserve of lead wire maintained inthe slack chamber.

According to yet another feature of the invention, automaticarrangements are provided for mounting spools of greater length foraccommodating greater storage length of lead wire for use in high speedautomatic bonding machines. The spool holder is provided with anoptically detectable index or slot. An index or slot detector withassociated counter and logic counts the rotations of the spool duringunwinding of lead wire for indicating that the spool is empty or in aspecified condition of depletion. An axial drive motor is also providedfor translating the spool in an axial direction to maintain the angle ofentry of lead wire from the spool into the inlet guide of the slackchamber within a desired angular range. The counting logic isoperatively coupled to the axial drive motor for actuating the axialdrive motor each predetermined number of rotations of the spool totranslate the spool along its axis a predetermined distance. The axialdrive motor also reverses the direction of axial drive for eachpredetermined number of turns of the spool corresponding to the end ofthe spool.

Other objects, features and advantages of the invention are set forth inthe following specification and accompanying drawings.

BRIEF FIGURE DESCRIPTION

FIG. 1 is a simplified diagrammatic view of an apparatus according tothe present invention for maintaining and feeding a slack reserve oflead wire in a bonding machine.

FIG. 2 is a diagrammatic plan view of the slack chamber with the topplate in open position showing the components of the slack chamber withlead wire appropriately threaded through the chamber

FIG. 2A is a diagrammatic front elevation view of the slack chamberlooking in the direction of the row of optical sensors shown in FIG. 2.

FIG. 2B is a detail of the flared ferrule used for wire guides in theslack chamber.

FIG. 3 is a block diagram of the spool rotary drive motor and associatedcontrol logic operatively coupled to the row of optical sensorspositioned in the slack chamber.

FIG. 4 is a mechanical diagrammatic view of the rotary drive motor andaxial drive motor couplings relative to the spool mounting device orholder with the drive belts partially cut away.

FIG. 4A is a detailed fragmentary side cross section of an alternatespool mounting device or holder.

FIG. 5 is a block diagram of the spool axial drive servomotor andassociated counter and control logic.

FIG. 6 is a block diagram of the slack chamber air flow control.

FIG. 7 is a schematic diagram of a typical optical sensor and detectorcircuit for use in the present invention.

FIG. 8 is a diagrammatic view of the lead wire configuration in theslack chamber of FIG. 2.

DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND BEST MODE OF THEINVENTION

The basic elements of a simplified apparatus for feeding and maintaininga slack reserve of lead wire for a bonding machine are shown in FIG. 1.The heart of the apparatus is a slack chamber 10 in which a length 12aof bonding lead wire 12 passing through the slack chamber from an inletferrule 14 to an outlet guide trough 15 is suspended under slighttension in a gaseous flow 16. The gaseous flow is typically dry air ornitrogen directed under pressure through an opening or tube leading intothe slack chamber 10. The bonding lead wire 12 is fed into the slackchamber from a spool 20 driven by motor 22 and drive belt 23. The slackreserve length of lead wire 12 is maintained within a predeterminedrange by the use of wire sensing elements 17 and 18 and the controllogic 24 responsive to the wire sensing elements. The sensor and controllogic 24 actuates drive motor 22 to initiate or terminate feeding ofbonding lead wire 12 into the slack chamber 10 from spool 20 in responseto signals received from wire sensing elements 18 and 17. The bondingwire 12 leads through the guide trough 15 at the outlet of slack chamber10 to the capillary bonding tool, not shown, mounted in the bonding headof the lead wire bonding machine. In the configuration of FIG. 1 thebonding wire 12 is fed or unwound from the side of the spool in adirection substantially perpendicular to the axis of the spool ratherthan being fed from the end of the spool in a direction parallel to thespool axis as required in conventional bonding machines.

Details of the novel wind pressure slack chamber according to thepresent invention are illustrated in FIGS. 2 and 2A. The slack chamber10 is comprised of a base 26 and hinge cover 28 shown in open positionin FIG. 2. The base 26 of slack chamber 10 includes the inlet ferrule 14provided with flared ends or tips to minimize physical injury ordeformation to lead wire 12. The outlet ferrule or guide trough 15 issimilarly seated in the base 26 of the slack chamber.

During threading of lead wire 12 through the slack chamber, the cover 28is of course in open position. With the cover in open position anextending and retracting threading post or wire holding post 30 extendsthrough a hole in the base 26 into the slack chamber 10. This threadingpost initially defines the length of slack reserve lead wire 12a along apath offset from an imaginary line 13 drawn between the inlet ferrule 14and outlet guide trough 15. The extending and retracting threading post30 thus defines a loop path for the wire as it is threaded by anoperator through the chamber 10. When the slack chamber cover 20 isclosed, the threading post 30 automatically retracts as shown in FIG.2A. The extension and retraction of post 30 may be mechanically actuatedby opening and closing motion of the cover 28 through appropriatemechanical linkages. Alternatively, the post 30 may be extended andretracted by a solenoid as hereafter described. The solenoid is in turnactuated by, for example, a microswitch 31 mounted on tab 32 extendingfrom the slack chamber base 26. Microswitch 31 is operated by a similartab 33 mounted on the cover 28.

To provide an indication of the exemplary dimensions of the reserve leadwire slack chamber 10 and the length of reserve lead wire maintained inthe slack chamber, FIG. 2 was drawn substantially to the actual scale ofan example device. During the initial threading the lead wire 12 isoffset in a slack reserve length 12a in a triangular configuration. Theslack reserve length is sufficient to provide a reserve for high speedautomatic operation of a ball bonding machine. Upon closing the slackchamber cover 28, the source of air or gas under pressure, not shown, isactuated, for example, by microswitch 31 for delivering a stream of dryair or gas. The air stream in blow tube or wind tube 35 is directedthrough an opening in the slack chamber in a direction across the slackchamber for maintaining the offset configuration of the slack reservelength 12a of lead wire 12 after retraction of the threading post 30.

The slack chamber 10 is provided with two sets of three optical sensors:1-1a, 2-2a, 3-3a; and 4-4a, 5-5a, 6-6a. The optical sensors are arrangedin a row along the axis of the maximum amplitude of offset of the leadwire 12 in the slack chamber. Each optical sensor includes a lightsource 1 thru 6 such as an LED mounted in the base 26 of the slackchamber and a photo detector such as a photo transistor 1a thru 6amounted in the cover 28 of the slack chamber in vertical alignment withthe respective LED.

As shown in FIG. 2, the first set of optical sensors 1-1a thru 3-3a ismounted in a row along the axis of offset of the lead wire adjacent tothe wind tube 35 and the imaginary straight line 13 connecting the inletferrule 14 and outlet guide trough 15. As hereafter set forth in furtherdetail, if the slack reserve length of lead wire 12a is depleting andthe amplitude of offset decreases to the point where the lead wirecrosses the space between the vertically aligned LED light source 1 andphoto transistor 1a, the shadow of the lead wire is detected and thesensor and control logic hereafter described actuates the spool drivemotor 22 rotating the spool 20 and delivering or incrementing the leadwire in the slack chamber 10. The increasing length of slack reservewire is suspended, offset and maintained in the air flow and theamplitude of offset increases.

A second row of optical sensors 4-4a through 6-6a is provided along theaxis of offset on the far side of the slack chamber away from the windtube 35. The sensor and control logic continues to actuate spool drivemotor 22 rotating spool 20 and feeding lead wire into the slack chamber10. The slack reserve length of lead wire increases as does theamplitude of offset until the crest of the offset configuration of leadwire crosses the space between LED light source 4 and photo transistor4a. The optical sensor 4-4a detects the shadow of the lead wire and thesensor and control logic as hereafter described shuts down spool drivemotor 22. Spool 20 ceases to feed lead wire into the slack chamber. Theslack reserve length 12a of lead wire 12 is therefore maintained withina specified range defined by the optical sensors 1-1a and 4-4a. Theoptical sensors 1-1a and 4-4a represent respectively the inner and outeror minimum and maximum amplitudes of the offset configuration of leadwire thereby defining or determining the range of length of the slackreserve.

As also hereafter described, back-up, redundancy or safety is built intothe apparatus for feeding and maintaining the slack reserve length oflead wire by providing back-up optical sensors. Thus, the first set ofoptical sensors 1-1a through 3-3a define the minimum length of the rangeof reserve lead wire and the minimum amplitude of offset. In the eventthe fine lead wire were to pass through the space of optical sensor 1-1afor some reason without detection, it would be nevertheless detected byoptical sensor 2-2a. Similarly, if it were to pass through opticalsensor 2-2a undetected or without actuation of the spool drive motor,then optical sensor 3 upon detecting the lead wire wire 12 would shutdown the bonding machine itself by actuating the emergency stop of thebonder and also shut down and stop the spool drive motor and any othermotor control in the apparatus for feeding and maintaining the reserveslack of lead wire. The second set of optical sensors 4-4a through 6-6adefine the outer limit of the range of length of the reserve lead wireand the maximum amplitude of the offset configuration. If the spool andspool drive motor continue to feed increments of lead wire into theslack chamber and the lead wire passes undetected through the space ofoptical sensor 4-4a, then it will be detected by optical sensor 5-5awhich will also shut down the spool drive motor. If the lead wire passesundetected through the space of optical sensors 5-5a, it will finally bedetected by optical sensor 6-6a which is also coupled through the sensorand control logic to shut down the spool drive motor upon detecting orsensing the lead wire shadow as hereafter described.

A detail of the inlet ferrule 14 for the slack chamber is illustrated inFIG. 2B. In FIG. 2 are clearly shown the flared ends of the ferrulewhich protect the fine capillary lead wire from damage. The lead wire,for example, is typically in the order of one mil in diameter. Theferrule is formed with polished inner surfaces. The ferru1e 14 is alsoprovided with a slot 14a for introducing fine lead wire into the ferruleduring threading of the lead wire through the slack chamber. The slot14a is accessible upon opening the cover 28 of slack chamber 10.Similarly, the outlet guide trough 15 is also provided with a threadingslot not shown for introducing the lead wire into the outlet guidetrough during threading.

A block diagram showing the electrical coupling of the optical sensorsand related apparatus shown in FIGS. 1 and 2 is illustrated in FIG. 3.The spool drive motor 22 is actuated by associated control circuitry andlogic 24 including a motor control unit 40 having "run" and "stop"inputs 41 and 42 respectively receiving control signals from OR gates 43and 44. OR gate 43 passes actuating signals from optical sensors 1-1aand 2-2a for actuating the motor control and turning on the spool drivemotor 22. As heretofore described with reference to FIG. 2, opticalsensors 1-1a and 2-2a detect the presence of lead wire 12 at the minimumamplitude range for the deflection of the lead wire reserve length 12aand actuate the spool motor to feed lead wire into the reserve chamberincreasing the deflection and amplitude of the offset configuration.Detection of the presence of the reserve lead wire length 12a by eitheroptical sensor 1-1a or 2-2a actuates the "run" input to the motorcontrol through the alternative OR gate 43. The manual control 45 allowsan operator to increase the slack reserve length of lead wire duringthreading through the slack chamber when cover 28 is open. Manualcontrol 45a turns off the spool drive motor.

OR gate 46 transmits shut down signals received from optical sensors3-3a and 4-4a through OR gate 44 to the stop input 42 of the motorcontrol unit for deactuating and turning off the spool drive motor 22.Similarly, OR gate 47 transmits shut down signals received from opticalsensors 5-5a and 6-6a through OR gate 44 to the "stop" input 42 of themotor control unit 40. Signals from optical sensors 5-5a and 6-6a willtherefore also shut down the spool drive motor and stop the feed of leadwire into the slack chamber. A signal from optical sensor 3-3a not onlyturns off the spool drive motor 23 but also shuts down the bondingmachine itself through lead 48 which is connected to the emergency stopinput of the bonder or bonding machine. Optical sensor 3-3a is locatedat the inner limit of range of the slack reserve length as thedeflection of the reserve length 12a approaches the imaginary straightline 13 between the lead wire inlet and outlet guides 14 and 15 of theslack chamber 10. If for some reason the lead wire is not detected inthe vicinity of optical sensors 1-1a and 2-2a as the lead wire slackreserve length is depleted, the optical sensor 3-3a will shut down thebonding machine to prevent breaking or severing of the lead wire untilan operator opens the slack chamber, actuates the spool drive motor andresets the offset deflection of lead wire around the extending andretracting post 30.

Optical sensors 4-4a, 5-5a and 6-6a respectively issue shut down signalsfor turning off the spool drive motor as the slack reserve length oflead wire and amplitude of deflection increase to the maximum limit ofthe permitted range. If for some reason optical sensors 4-4a and 5-5afail to sense or detect the lead wire as the deflection amplitudeincreases during feeding of lead wire into the slack chamber, thenoptical sensor 6-6a provides a final back-up and safety for turning offthe spool drive motor. Thus, the sensor and control logic of FIG. 3affords calculated redundancy in the form of successive back-up safetycontrols for maintaining the slack of reserve wire within the minimumand maximum limits of the desired range of length.

Details of a mechanical arrangement for mounting a spool of lead wireand for controlled feeding of the lead wire into the slack chamber isshown in FIGS. 4 and 4A. The spool 20 is mounted for rotation about thespool axis on a drive shaft 50 including a slotted disk 52 which rotateswith shaft 50 and spool 20. The shaft is mounted for rotation onbearings 53 on a carriage and mounting plate 54. The spool drive motor22 is similarly mounted on the carriage plate 54 and rotates the shaft50, slotted disk 52, and spool 20 by means of the timing belt, notchedbelt or chain 23 mounted respectively on the belt wheels 56 and 57 ofthe drive shaft of motor 22 and rotating shaft 50. The use of a notchedbelt or timing belt maintains registration between the turning of thespool drive motor 22 and the turning of the slotted disk 52.

The carriage plate 54 is in turn supported, mounted and journaled fortranslation on the threaded rods 60 and 61 which rotate within framepieces of the stationary base or frame 62. Threaded rods 60 and 61 aredriven in rotation by axial drive motor 65 mounted on the stationarybase 62 and provided with a belt wheel 66 at the end of its drive shaft67. Axial drive motor 65 turns the journaled shafts 60 and 61 by meansof the drive belt 68 which engages belt wheels 70 and 71 fixedrespectively to the journaled shafts 60 and 61. A slotted disk 72 isalso provided on the drive shaft 67 of the axial drive motor 65. Drivebelt 68 is also a notched belt, timing belt or chain to maintainregistration between the turning of slotted disk 72 and the turning ofthreaded rods 60 and 61.

By this apparatus arrangement, the objective of the present invention isachieved of feeding the lead wire 12 from spool 20 at all times tangentto the cylinder of the spool and perpendicular to the spool axisrepresented by shaft 50. As shown in more detail in FIG. 4A, the shaft50 terminates in a spindle 74 on which the spool is mounted byfrictional fitting so that spool rotates with the shaft. While spooldrive motor 22 rotates the spool 20, feeding the fine bonding lead 12into the slack chamber 10, axial drive motor 65 is coordinated throughthe logic circuitry of FIG. 5 hereafter described to translate thecarriage 54 and maintain the lead wire 12 feeding from the spoolsubstantially at right angles to the spool axis and tangent to the spoolcylinder. A feature and advantage of this mechanical and controlcircuitry arrangement is that the very fine lead wire exiting the spoolis not drawn over underlying layers thereby eliminating damage to ordeformation of the lead wire. According to conventional procedures forfeeding lead wire from the end of the spool in the direction of thespool axis, a gold lead wire spool is limited to a single layer becauseof the deformation which would otherwise occur to the underlying layer.According to the method of the present invention, multilayered spoolsmay be used storing greater lengths of wire and requiring less frequentchange of spools. Furthermore, by use of the translating carriage 54 aspool 20 of greater length may be used while still maintaining alignedfeed of the lead wire from the spool in a direction tangent to the spoolcylinder and perpendicular to the spool axis. To isolate the bondingwire and spool electrically from ground for certain applications, thespool mounting assembly or holder is composed of or in turn mounted oninsulating material using a rubber drive belt between the spool anddrive motor.

Referring both to FIGS. 4 and 5, the spool disk 52 mounted on shaft 50rotates with spool 20 and is formed with a slot which is detected byslot detector 80. The slot detector 80 provides a signal each time theslot and spool rotate 360° for counting the turns of wire fed from thespool by a downcounter and comparator 81. The downcounter 81 is presetfor indicating depletion of the spool by indicator 82 after a presetnumber of turns have been counted. At the same time the signals from theslot detector 80 are also input to a divide by "Y" circuit 83 foractuating the axial drive motor 65 each "Y" number of turns to maintainan axial translation of the spool 20 commensurate with the lateraldepletion of turns of wire.

Coordination between the spool drive motor 22 and axial drive motor 65is achieved by the coordinated use of the second axial drive slotdetector 84 which detects the slot in axial drive motor disk 72 for each360° rotation of the disk 72. The signal from axial drive slot detector84 is fed to a divide by "X" circuit 85 which provides a signal each "X"number of rotations of the disk 72 through OR gate 86 to stop the axialdrive motor 65. In this example embodiment of the present invention, "Y"equals the number of turns of wire on spool 20 per unit length, while"X" equals the number of turns of the thread of threaded rods 60 and 61per unit length. The control circuitry of FIG. 5 therefore equalizes thetranslation of carriage 54 in the axial direction of spool 20 with thedepletion of turns of lead wire in the axial direction of the spool.Typically, the number of turns of wire "Y" per unit length isconsiderably greater than the number of threads "X" per unit length ofrods 60 and 61 so that a few turns of rods 60 and 61 by axial drivemotor 65 provides the same axial distance as many turns of spool 20driven by spool drive motor 22. The selection of the numbers "X" and "Y"for a particular application may be input to the respective dividecircuits 85 and 83 by thumb wheel switches.

Control of the direction of rotation of axial drive motor 65 andtherefore the direction of translation of carriage 54 is achieved bylimit switches 87 and 88. Contact of carriage 54 with limit switch 87initiates a signal through directional control logic 90 to reversedirection of axial drive motor 65 and commence movement of the carriagein the down direction. Contact of carriage 54 with microswitch 88initiates a signal through directional control logic 90 to reverse theaxial drive motor 65 and commence motion of carriage 54 in the upwarddirection. Upper limit microswitch 91 provides an emergency stop shouldthe carriage for some reason proceed beyond microswitch 87. Lower limitmicroswitch 92 provides a lower limit emergency stop signal shouldcarriage 54 for some reason proceed beyond microswitch 88. The emergencystop signals from outer limit switches 91 and 92 pass through OR gate 93and OR gate 86 to the axial drive motor 65.

The airflow system and airflow control for maintaining the slack reserveof lead wire in offset configuration under slight tension is shown inFIG. 6. Pressurized dry air or nitrogen from a source 100 is regulatedby flow control 101 and admitted into the wind tube 35 of the slackchamber 10 by means of a solenoid valve 102. Solenoid valve 102 may be,for example, an electrically actuated solenoid valve or a pneumaticallyor air actuated solenoid valve which admits air into the wind tube orblow tube 35 leading into the slack chamber and shuts off the air flowwhen the valve is closed. The pressurized air or nitrogen from source100 is appropriately processed and dried to prevent corrosion ordeterioration of the fine metal wire suspended in the slack chamber airflow. The dry air or nitrogen in fact serves to clean the lead wire.

The solenoid valve 102 is opened by driver 104 when a signal is receivedfrom AND gate 105. A signal appears at the output of AND gate 105 whensignals coincide at the AND gate inputs from the microswitch 31 in theslack chamber and clamp signal 106 originating in the ball bondingmachine. Clamp signal 106 indicates that the lead wire is being held byclamps in the bonding head so it will not pull out when the air streamis initially applied in slack chamber 10. Microswitch 31 provides asignal upon closing of the cover or lid 28 over the base 26 of slackchamber 10. The microswitch signal generated by closing the slackchamber, coinciding with clamp signal 106 at AND gate 105 may also beused to actuate a separate solenoid 108 through driver 107 forretracting the extending and retracting post 30. Alternatively, theretracting post may be actuated by the mechanical motion of the slackchamber cover lid 28.

The air flow through wind tube or blow tube 35 directing a wind orstream of air into the slack chamber along the row of two sets ofoptical sensors should be sufficient to suspend and maintain the slackreserve length of lead wire under slight tension in untangled condition.However, the force on the wire due to the velocity and volume of airflow should be less than the holding or clamping forces on the lead wirein the vicinity of the bonding head afforded by the particular bondingmachine. More generally, the force on the slack reserve length of leadwire due to wind pressure should be kept down to a level that does notinterfere with the bonding and welding operations of the particularmachine. Specifically, the force on the wire due to wind pressure mustbe small enough not to interfere in bonding operations during so-called"looping" from the ball bond to the weld or wedge bond and must be lessthan the holding, clamping or drag forces on the wire provided by thebonding machine in the vicinity of the bonding head.

The fine bonding lead wire is typically 1 to 1.15 mil wire. For thisfine wire a blow tube or wind tube 35 of, for example, 1/8 inch (0.3 cm)outer diameter (o.d.) has been found sufficient with pressure for thedried air or nitrogen in the order of, for example, 10 to 50 psi. Thevolume of air flow is therefore so small that the air flow or wind maybe left on at all times, for example, overnight and on weekends orbetween operating shifts of the bonding machine. For example, 12standard cubic feet per hour (scfh) of dry nitrogen at 30 psi through1/8 inch (0.3 cm) o.d. tubing is sufficient. In this manner, the slackreserve length of lead wire may be maintained at all times under slighttension and in untangled condition. The air flow may therefore remain onat all times until a particular spool is depleted.

The usual wire length in conventional spools, for example, of fine goldbonding lead wire is 330 feet (100 m) and the spool requires frequentreplacement. According to the apparatus and method of the presentinvention, an elongate spool may be used with greater capacity andseveral layers of wire for a total length of, for example, 1,000 (300 m)to 1,500 feet (457 m). According to the present invention spoolreplacement is therefore less frequent and the air flow simply remainson maintaining the slack reserve of lead wire under slight tension andin untangled condition until the spool of greater capacity is depleted.As an additional feature a separate emergency power supply such as aback-up battery may be provided for the air supply system to maintainthe air flow in the event of loss of power. Similarly, the back-up powersupply may be available on standby for the entire bonding lead wire feedand reserve maintenance equipment to preserve, for example, the countingmemory of the sensor and logic control circuitry to keep track of thestate of depletion of the spool in the event of loss of power.

In the slack chamber cavity construction, black anodized aluminum, forexample, may be used on the inside bottom of the chamber. The LED lightsources 1 thru 6 are positioned in the base 26 looking up from thebottom and are typically infrared light sources. The infrared sensitivephoto transistors 1a thru 6a are positioned on top respectively alignedwith the LED light sources 1 thru 6. The typical circuit for eachoptical sensor or optical detector 1-1a thru 6-6a is illustrated in FIG.7. The LED infrared emitter 1 appropriately juxtaposed relative toinfrared detector photo transistor 1a are coupled in a detector circuitwith operational amplifier 110 which may be, for example, an LM 324 opamp. The op amp 110 compares the voltage across the voltage dividernetwork 112 including the variable potentiometer R₅, to the voltage dropacross R₂. The voltage drop across R₂ changes with the presence of leadwire between infrared emitter 1 and infrared detector 1a. Thepotentiometer R₅ sets the threshold at which the output 114 switchesfrom normally low state to high state when the infrared beam isinterrupted by the lead wire. The optical sensor output at terminal 114therefore switches from the normally low voltage state to high when theinfrared beam is interrupted.

During high speed ball bonding and wedge bonding operation, it isimportant to maintain a sufficient reserve length of lead wire inuntangled condition to meet successive bonding operations. This may beaccomplished with a slack chamber having dimensions, for example, of 10cm square. With a slack chamber of these dimensions and in theconfiguration of FIG. 2, Table I summarizes in Column F the slackreserve length 12a of lead wire available for each of the differentangles θ of offset from the imaginary line 13. The lead wireconfiguration in the chamber is shown diagrammatically in FIG. 8. InTable I Column A lists the successively greater amplitudes incentimeters corresponding to the successively greater angles θ ofoffset. Amplitude is the distance between the peak or crest of thetriangular offset configuration and imaginary line 13. The distance Xrepresents half the width of the slack chamber or 5 cm with x² =25 cm.The hypotenuse of the right triangle formed by the reserve length oflead wire in each half of the slack cavity is shown in Column D for eachdifferent angle of offset θ as calculated from Columns B and C. Theactual slack reserve length of lead wire in each half of the slackchamber, that is the left half and right half is indicated in Column Ewith Column F showing the full slack reserve length from the two righttriangles in each half of the slack chamber. Thus, if the initial angleof offset of the lead wire 12 entering the slack chamber is 61° and theangle of offset is reduced to 58° as a result of bonding operations, thelength of lead wire depleted is 10.6 cm minus 8.8 cm or approximately1.8 cm. If the angle of offset is reduced from 61° to 55° by reason ofdepletion of the lead wire through bonding operations, the length oflead wire withdrawn is approximately 3.4 cm. This corresponds to a 2 cmreduction in the amplitude of offset of the peak of the offsetconfiguration. In this manner, the offset can initially be adjusted toafford the slack reserve length of lead wire necessary to accommodatethe speed of operation of the particular ball bonding machine. It isfound that an optimum angle of entry for the slack reserve length 12a isbetween 50° and 60°. A transparent cover 28 may be provided over thewind chamber cavity or slack chamber 10 for a visual check of the statusof the slack reserve length of lead wire.

While the invention has been described with reference to particularexample embodiments, it is intended to cover all variations andequivalents within the scope of the following claims.

                  TABLE I                                                         ______________________________________                                                                         SLACK                                                    x.sup.2 +                                                                            x.sup.2 +     RESERVE ⊖                            y    y.sup.2                                                                              y.sup.2                                                                              y.sup.2                                                                            x.sup.2 + y.sup.2 - x                                                                  LENGTH  tan.sup.-1 y/x                       ______________________________________                                        1     1     26     5.1  0.1      .2      11°                           2     4     29     5.38 0.38     0.76    22°                           3     9     34     5.83 0.83     1.66    31°                           4    16     41     6.40 1.40     2.80    39°                           5    25     50     7.07 2.07     4.14    45°                           6    36     61     7.81 2.81     5.62    50°                           7    49     74     8.60 3.60     7.20    55°                           8    64     89     9.43 4.43     8.86    58°                           9    81     106    10.3 5.3      10.6    61°                           10   100    125    11.2 6.2      12.4    64°                           ______________________________________                                    

We claim:
 1. An apparatus for feeding bonding lead wire from an elongatespool to the capillary wire holding tool of a lead wire bonding machinecomprising:spool mounting means constructed and arranged for mountingthe spool for rotation around the spool axis; spool motor means coupledto the spool mounting means for rotating a spool about the spool axis;control means operatively coupled to the spool motor means for actuatingsaid spool motor means and advancing lead wire from the spool inpredetermined increments; axial drive motor means operatively coupled tothe spool mounting means for translating said spool in an axialdirection to maintain the angle of feeding of lead wire from the spoolwithin a desired angular range; said spool mounting means comprising arim having index means formed thereon, spool rotation sensor meansoperatively mounted and coupled to the spool mounting means fordetecting the index means upon rotation of the spool and for generatingcorresponding signals, counting logic means operatively coupling saidspool rotation sensor signals and the axial drive motor means foractuating said axial drive motor means each predetermined number ofrotations for maintaining the wire feeding from the spool substantiallyat right angles to the axis of the spool.
 2. The apparatus of claim 1wherein said spool mounting means comprises a rim which rotates with aspool mounted on the spool mounting means, said rim formed withoptically detectable index means, said spool rotation sensor meanscomprising rim optical sensor means operatively mounted in stationaryposition for sensing the index means upon each rotation of the spool andfor generating corresponding signals, said counting logic means beingoperatively coupled for counting said corresponding signals and hencethe number of rotations during unwinding of a spool mounted on the spoolmounting means, and indicator means operatively coupled to said countinglogic means for indicating that the spool is empty or in a specifiedcondition of depletion based upon the counted number of rotations. 3.The apparatus of claim 1 further comprising directional control meansoperatively coupled for reversing the direction of axial translation ofa spool mounted on the spool mounting means by the axial drive motormeans.
 4. The apparatus of claim 1 further comprising first timing beltmeans operatively registering the turning of the spool motor means andspool mounting means and second timing belt means operativelyregistering translation by the axial drive motor means.